250cc D7 misfiring

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cann0nf0der

cann0nf0der

Active Member
Joined
Jun 20, 2010
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Location
Kellyville, Sydney
Hi all

Have a new Mikilon D7 250cc that has only done one tank of 91 gas. Just filled up (98 octane this time)for the second runin tank and now it is just misfiring badly under load. Idles fine but can detect slight misfire go for a run and basically low to medium revs it just misfires like mad.

Pulled the plug and it is light grey like it is running too lean. Have change the plug to a NGK D8EA 2120 but exactly the same problem.

Thought it would run a bit better on 98..... Should I only be running 91?

Any assistance appreciated
 
drain the fuel and try the lower grade fuel... if the carb is tuned lean then it will be very noticeable with higher octane
also check your valve clearance
 
OK I have tried the following:

1. Set the valve clearances .0051mm (there was basically none before)
2. Changed the fuel to 91
3. set the spark gap .61mm
4. Bled the carby
5. Changed the fuel filter

Still has a bad miss at about 1/4 throttle and above. If I accelerate slowly it isn't quite as bad. Being a brand new bike I am at a loss so any input very welcome.

BTW: Has a factory fitted JINKE carby
 
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sounds like jetting problems to me, although it might not be since the bike is brand new and has had no tuning done to it
 
since it seems you have checked the basics maybe time to completely disassemble the carby and blow it out with air and reseal all manifold gaskets and check the exhaust is sealing properly in the head..

failing that its time for a proper carby tune... so firstly id suggest you drop the needle clip by 1 notch
also is the carby a pumper style one?
and can you post jet sizes when/if you pull it apart..
 
I have checked the exhaust is sealing, so might pull the carby down. Not sure on pumper style... more of a car mechanic than bike so have attached pics.

2wqfmah.jpg


3r5n7.jpg
 
it's coughing becuase the jetting is out. The Main jet supplied standard with these is by memory, a 135 main.... which is massively too big.
Go back to a 95-100 main jet, the bike will run a lot better...
and make sure you have the choke operating the right way.... caught me out the first couple of rides with the blitz...
 
OK Main jet on the left below is 102 and the next one to the right is 37

15wmhae.jpg

16t8c1.jpg

21jch20.jpg


Have pulled it apart fully cleaned and checked the jets were all clean etc. Restarted the bike same issue, it is running very lean I am sumizing given the state of the brand new plug below. Have tried to richen it up as much as I can but makes the problem worse.

2em0wnb.jpg


I have rechecked valve clearances and all seems OK. I did notice ATDC for opening neither valve is fully open, see below. Is this right?

zk1r9x.jpg


hu4s3t.jpg
 
hmm ok so mikilon actually listened and changed the jets in these standard.... so the jetting should be ok...
when the bike has warmed up, whereabouts do you have the choke lever positioned? up, or down? chock off position, is with the lever DOWN... sounds simple, but has caught a few people out, including myself when i first got the bike..
aside from that, i cant think of a decent reason for it to be coughing, if the jetting is ok and valve clearances are ok...
have u tried raising the e-clip on the needle at all?
 
If you mean the big air needle that comes in from the top, no I haven't tried that, does it have extra notches on it that the clip fits into? or does it just grip tight to the needle?
 
if you undo the carby top, and remove the slide from the cable/spring etc, there is a needle inside the slide with a clip on the top, and the needle will have multiple grooves on it, that the clip attaches to...
if you move the clip UP it will richen the mixture, if you move the clip DOWN it will lean out the mixture...
 
in picture 5, is that where you set the valve clearances?
if so then you have set them with the cam on the rock.. you need to roll the engine around 360 degree's to get the cam in the correct location..

and yep id be dropping the cir-clip on the slid needle 1 slot at a time till you get it running nicely..

oh and thump.. you have your clip info back to front lol.. too many rums????
 
If you mean the big air needle that comes in from the top, no I haven't tried that, does it have extra notches on it that the clip fits into? or does it just grip tight to the needle?
 
what do you mean by air needle.. unscrew the slide from the top of the carby and there will be a long needle hanging out the bottom of it..
to adjust it you need to remove the throttle cable and push the needle out..
 
Ok onto where you are going, current sitting on the middle grouve out of 5 so have moved down one and will give that a go tomorrow (leave the neighbors in piece this evening :) )

I think you did mention this in your first post Sean, I just didn't know what you meant :)

Thanks again for all the help will let you know how I get on.
 
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